1. Field of the Invention
The present invention relates to an image processing system, an image processing method, and a computer program for analyzing an input image and outputting a monitoring result.
2. Description of the Related Art
There is an image processing system that analyzes an image obtained by photographing a predetermined area with a monitoring camera and detects a moving body such as a person or a car to thereby perform monitoring (hereinafter referred to as monitoring system).
FIG. 9 is a diagram of a state of moving body detection in such a monitoring system. A monitoring camera (not shown) photographs, from the front, a person 51 as a moving body and a sign 52 as a background object located behind the person 51. The person 51 is captured in a moving body detection frame 53 as an object to be monitored. In such moving body detection processing, it is possible to apply an algorithm for calculating temporal changes in pixel values in an image and, when a difference among the pixel values is equal to or larger than a predetermined value, determining that a moving body is present in the image (see JP-A-2006-107457).
As shown in FIG. 9, the person 51 as the object is passing in front of the sign 52. No temporal change occurs in the sign 52 because the sign 52 is stationary. Only the person 51 is captured in the moving body detection frame 53 and detected by the monitoring camera.
In this example, a moving body is not limited to the person 51 and may be, for example, a car or a bicycle. The background object 52 may be, for example, a house or a tree.
As shown in FIG. 10, when the sunlight is irradiated on a pole 521 of the sign 52, the sunlight is reflected on an area 522 on the surface of the pole 521 and causes a large luminance change. The same phenomenon occurs if a background object is an object having a surface that, like the sign 52, causes reflection of light such as a wall surface of a warehouse made of metal or a curbstone. Although the sign 52 is not moving, a luminance change in the sign 52 is large. Therefore, such light reflection is misdetected as an object via the monitoring camera in the moving body detection algorithm.
FIG. 11 is a diagram of a state in which the person 51 passes a sunlight-irradiated side of the sign 52. As shown in FIG. 11, when the sunlight is blocked by the person 51, a shadow 523 is formed in a part of the area 522 on the surface of the pole 521. In this case, the luminance on the surface of the pole 521 substantially changes. Although the person 51 is not passing between the monitoring camera and the sign 52, a luminance change is large on the person 51. Therefore, such a shadow is misdetected as an object via the monitoring camera in the moving body detection algorithm.
Such misdetection may occur at night. Normally, as shown in FIG. 12A, light is not emitted from the surface of the pole 521 of the sign 52 at night. However, as shown in FIG. 12B, when some light such as light of a car is irradiated on the pole 521, the light is reflected on, for example, an area 524 on the surface of the pole 521 to generate reflected light. In such a case, as in the case explained above, although a moving body such as the person 51 is not passing between the monitoring camera and the sign 52, a luminance change is large. Therefore, the reflected light is misdetected as an object via the monitoring camera in the moving body detection algorithm.
Therefore, in the moving body detection algorithm in the past, for example, as shown in FIG. 13, processing for setting a mask area 54 in a position of the pole 521 of the sign 52 as a non-detection area to not perform image processing in the mask area 54 is performed. This makes it possible to prevent misdetection on the surface of the pole 521.
Another related art includes Japanese Patent No. 3997062.